Process for achieving a controlled gradient density coating on a light attenuation medium

ABSTRACT

Process is disclosed for disposing a patterned light attenuating coating of a differential density on a substantially transparent optical medium, used in the optical system for photoforming the windowed interstitial web portion of a color cathode ray tube composite screen structure. The process utilizes a hermetic chamber wherein there is included a vaporizing source, a rotatable first pattern mask, a movable second pattern mask, support means for positioning the optical medium, and optical means for monitoring the deposition of coating thereon. The process achieves the deposition of a nonsymmetrical coating formed to modify the photo-exposure illumination from the photoexposure light source.

ll-ZO-73 XR 3 7735541 Unlted States Patent 1191 1111 3,773,541

Ng et al. Nov. 20, 1973 PROCESS FOR ACHIEVING A 2,341,827 2 1944 Sukumlyn 118/49 x CONTROLLED GRADIENT DENSITY 2,384,578 9/ 1945 Turner 350/314 X 3,503,781 3 1970 Forman et al. 118 49.1 x COATING ON A LIGHT ATTENUATION 3,561,993 2 1971 Geffcken 117/38 MEDIUM 3,117,885 1 1964 Pohm 118 49 x 75 Inventors: David M N Charles H. Rehkopf, 3,442,572 5/1969 lllsley 7/38 X both of Seneca Falls, N.Y.

Primary Examiner-William D. Martin 1 g GTE Sylvania Incorporated, Seneca Assistant ExaminerWilliam 11. Schmidt Falls N-Y- Att0rney-Norman J. OMalley et al.

[22] Filed: Feb. 7, 1972 21 l N 2 3 1 [57] ABSTRACT 1 App 2 0 Process is disclosed for disposing a patterned light at- Related US. Application Data tenuating coating of a differential density on a sub- [62] Division of Sen No, 030 Nov, 2 1970 Pat, stantially transparent optical medium, used in the opti- 3,664,295. cal system for photoforming the windowed interstitial web portion of a color cathode ray tube composite [52] US. Cl. l17/33.3, 95/1 R, 117/38, screen structure. The process utilizes a hermetic 117/107, 350/314 chamber wherein there is included a vaporizing [51] Int. Cl C231: 13/02, G02b 5/22 source, a rotatable first pattern mask, a movable sec- [58] Field of Search 95/1 R; 350/314, ond pattern mask, support means for positioning the 350/320, 195; 117/107, 38, 33.3; 118/7, 8, optical medium, and optical means for monitoring the 4849.5, 504, 505, 301 deposition of coating thereon. The process achieves the deposition of a nonsymmetrical coating formed to [56] References Cited modify the photo-exposure illumination from the UNITED STATES PATENTS ph0to-exp0sure light source.

2,160,981 6/1939 OBrien 118/49 X 4 Claims, 10 Drawing Figures 7 IO8---1 I67 /65 PATENIEUMOVZO 197s 3; 773. 541

T0 vAcuuM PuMP PAIENTEDunv 20 I973 uv TRANSMISSION (PERCENT) uv TRANSMISSION (PERCENT) 3.773.541 SHEET 30F 4 O l 1 I l l 2.5 '20 /.5 /.O -.5 0 .5 /.O /.5 2.0 2.5

.D/AMETEICAL. LENS DIMENSION ALONG Y AXIS (INCHES) O I 1 I 1 -25 -20 -/.5 -/.o .5 0 .5 /.o /.5 2-0 2.5

.lD/AMETRICAL LENS DIMENSION ALONG x Ax/s (INCHES) /39 F] g. 5

PROCESS FOR ACHIEVING A CONTROLLED GRADIENT DENSITY COATING ON A LIGHT ATTENUATION MEDIUM CROSS-REFERENCES TO RELATED APPLICATIONS This application is a divisional application of U.S. Pat. Ser. No. 86,030, filed Nov. 2, 1970 now U.S. Pat. No. 3,664,295, which is assigned to the assignee of the present invention.

This divisional application contains matter disclosed but not claimed in a related co-pending U.S. patent application assigned to the assignee of the present invention. This related U.S. Pat. application is Ser. No.-

86,123, filed Nov. 2, 1970, now U.S. Pat. No. 3,667,355 titled: Optical System For Forming a Windowed Web In A Color Cathode Ray Tube Screen Structure."

BACKGROUND OF THE INVENTION This invention relates to cathode ray tubes and more particularly to the process for disposing a discrete light attenuating coating on an optical medium utilized in an optical system for photo-forming a color cathode ray tube composite screen structure.

Cathode ray tubes capable of presenting multi-color display imagery, such as those utilized in color television applications, conventionally employ patterned screens which are comprised of an orderly array of separate color fields formed of repetitive groups of related hue-emitting phosphor materials. As an example, in the well-known shadow mask type of tube construction, the color screen pattern is conventionally made up of a vast multitude of discrete dots formed of selected cathodoluminescent phosphors which are usually arranged in triad relationship. Such dots upon selective electron excitation, emit predetermined additive primary hues to produce the desired color imagery. Associated with the screen within the tube envelope, is a foraminous structure or shadow mask having multitudinous apertures therein. Each of these apertures is related to a specific grouping or triad of dots comprising the color screen pattern, and spaced therefrom in a manner to enable the selected electron beams, traversing the apertures, to impinge the proper dots therebeneath.

To enhance color purity, improve brightness and accentuate contrast of the color screen image, an advantageous composite screen structure has been developed, wherein a dot-defiining interstitial spacing is provided between the individual dots in the form of an opaque light-absorbing material. In essence, each of the phosphor dots comprising the screen pattern is encircled or defined by a substantially dark interstitial encompassment which collectively forms a multi-opening pattern or windowed webbing having substantially opaque interstitial connections. It is imperative that these definitive windows be of proper sizes and in precise orientation with reference to the individual phosphor dots at the areas of respective beam impingement.

Fabrication of the windowed interstitial webbing is accomplished either before or after phosphor screening by several processes wherein photo-deposition techniques play a prominent role. The exposure devices and associated optical systems employed in fabrication of the windows resemble those utilized in phosphor dot formation. Conventionally, these include an exposure light source and a refractive component or lens oriented in a manner to provide light optics intended to substantially duplicate the electron optics of the operating tube. It has been found that the optical preciseness necessary for fabricating the desired window pattern of the composite screen structure is not inherently available in the usual phosphor screening exposure systems. This lack of optical precision is sometimes evidenced by the non-uniformity of the electron-excited white field in various portions of the windowed screen in an operating tube. Such off-white areas are found to be due to a subtractive effect produced by a smaller than desired size of one of the related tri-dot windows, i.e., red, blue, or green in certain areas of the screen. The presence of this smaller window also aggravates misregistration or eclipsing of the impinging beam by a portion of the opaque interstitial material defining the window which adds to the undesirable off-white effect. Thus, the phosphor defining windows become additional determinant factors influencing the contrast, brightness and color quality of the excited screen area. This emphasizes the fact that advancement in the art of producing improved color cathode ray tubes brings with it an imperative need for improved precision and refinement in screen fabrication means and techniques.

In the windowed-structure color screen, it is desired to have a variable gradient of window sizes from center to edge of the screen, and in addition, the windows should be of substantially equal size in annular orientation prgressively about the central axis of the screen. The coated optical components commonly utilized in the window exposure optical systems usually employ light attenuation coatings having substantially symmetrical light transmission characteristics, i.e., a plot of percent light transmission versus distance from center to edge of the coated optical component varies inversely as the square of the distance from the source. A common type of apparatus for disposing such light attenuation coating may utilize a diametrically controllable iris mask which usually does not readily lend itself to the deposition of a differential nonsymmetrical pattern.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to reduce the aforementioned disadvantages and to provide an improved process for achieving a controlled gradient density attenuating coating on an optical medium employed in an optical system for photoforming a color CRT composite screen structure.

The definition of the term density as used herein refers to the opaque quality of the coating.

The foregoing objects are achieved in one aspect of the invention by an improved process for vapor disposing a light attenuating coating of a controlled gradient density on a substantially transparent optical medium. The technique involves positioning the to-be-coated optical medium in a hermetic chamber in a manner that a metal vaporizing source is oriented in spaced relationship with the side of the medium to be coated. Posithe rotatable mask in a manner to enable insertion and removal of the second mask into and out of the modified vapor beam to effect secondary modification of the beam. Operationally, when the vapor deposition through the rotatable first pattern mask exhibits light attenuation of a predetermined level, the fixed pattern of the second mask is moved into the modified vapor beam to further control the vapor deposition and provide the desired composite nonsymmetrical attenuation coating pattern on the optical medium.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a color cathode ray tube of the shadow mask type employing a windowed composite screen;

FIG. 2 is an enlarged fragmentary view of the screen as seen through the viewing panel by an observer;

FIG. 3 is a plan view of an exposure apparatus employed in photo-forming the multiple window portion of the composite screen structure;

FIG. 4 is a plan view of the coated optical medium utilized in the exposure apparatus taken along the line 4-4 of FIG. 3;

FIGS. 5 and 6 are profile representations of the UV transmission of one embodiment of the compositeattenuation coating disposed on the surface of the optical medium taken along the lines 5-5 and 6-6 of FIG. 4;

FIG. 7 is a cross-sectional view of the apparatus for vapor disposing the light attenuating coating on the optical medium;

FIG. 8 is an isometric view detailing certain of the cooperating means shown in FIG. 7;

FIG. 9 is a plan view illustrating an embodiment of the configurative opening in the rotatable first pattern mask; and

FIG. 10 is a profile representation of the light transmission of the attenuation coating at substantially the central portion of the optical medium during formation of the coating pattern thereon.

DESCRIPTION OF THE PREFERRED EMBODIMENT For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following specification and appended claims in connection with the aforedescribed drawings.

The need for and utilization of a specialized nonsymmetrical composite pattern of light attenuation coating is presented as a background for adequately considering the means and process of achieving the desired discrete coating pattern.

With reference to the drawings, there is shown in FIG. 1 a conventional shadow mask type of color cathode ray tube 11 having a central axis 13 therethrough. Suitably positioned within the neck portion. 14 of the envelope 15 are three electron guns l7 oriented, for example, substantially 120 apart and equally spaced about the central axis 13 to provide a delta arrangement of electron beams 19, 21 and 23, respectively. The several beams are directed to converge at the apertured shadow mask 25, and thence pass through the apertures 27 therein to discretely impinge the composite screen structure 29 spaced therebeneath. The composite screen 29, which is disposed on the interior surface of the viewing panel 31 comprises a multiple window pattern 33 formed on an opaque interstitial webbing 35 that discretely defines the multitudinous window areas 37. Disposed relative to the window areas 37 are a multitude of triadically arranged dots 39 of red, blue, and green color-emitting electron responsive phosphor materials.

Since the tube axis, and panel axis are substantially coincidental, it seems expedient for clarification to denote these respective axes as the central axis 13.

With particular reference to FIG. 2, an enlarged fragmentary section of the screen is illustrated as seen from the viewpoint of an observer 41, facing the front of the view panel 31. The phosphor areas available for utilization informing the visible display, on the composite screen 29, are determined by the respective areas of the defining windows 37 in the interstitial webbing 35. The geometry of the tube 11 is such that the three electron beams 19, 21 and 23 make landings to form a substantially triadical formation on the screen. One such grouping is shown in FIG. 2. To adequately utilize the beam landings, the respective phosphor window areas 37 should coincide therewith. As previously mentioned, such was not always true especially when the optical system conventionally utilized for phosphor dot exposure was used for window fabrication. Often a resultant difference in size of one of the windows in the triad was evidenced in certain portions of the screen.

It has been found that the smaller sized window in the triads can be increased as desired to equal or be proportional to the other window areas in the respective triadical groupings. This is accomplished by incorporating an improvement in the optical system employed in photo-forming of the multiple window pattern. The improvement is in the form of related light attenuation coating patterns of differential nonsymmetrical density that are disposed relative to the lens in the optical system to discretely effect the exposure illumination passing therethrough. This provides a variable gradient of screen window sizes from center to edge of the screen and effects substantially constant window sizes in annular orientation progressively about the central axis 13.

Optical exposure means, such as that shown in FIG. 3, is employed to photo-form the multiple window pattern of the opaque interstitial web ofa composite color cathode ray tube screen structure. The basic features of the optical system are similar to those disclosed in U.S. Pat. No. 3,509,802, issued to Glen A. Burdick and assigned to the same assignee as the present invention. Another related optical system is disclosed in U.S. Pat. No. 3,448,667 issued to H. E. Smithgall and assigned to the same assignee as the present invention.

Prior to the exposure of each of the respective window patterns, the inner surface of the viewing panel 31 is coated with a light hardenable photosensitive substance 43 such as dichromate sensitized polyvinyl alcohol. The apertured shadow mask 25 is temporarily positioned in spaced adjacency with the sensitized panel, whereupon the mated mask-panel assembly is positioned on the exposure apparatus 45. Within the exposure apparatus, there are means 47 for predeterminately positioning an optical system 49 comprising: a primary source of exposure illumination 51, an associated light source collector rod 53, a modified planoconcave lens 55, and a two pattern composite light attenuation coating 57 disposed relative to a surface of said lens 55. For purposes of illustration, the profile of the composite lens coating 57 is exaggerated in FIG. 3. Actually, the composite coating is of substantially neutral density, for example, a thin vapor disposed metallic coating of a suitable metal or alloy having varied thickness and exhibiting discrete degrees of opacity. This metallic coating should be of a neutral density within the spectrum of light utilized in photo exposure, and exhibit stability under atmospheric conditions. Nickelchromium alloys, such as Inconel, which is available from the International Nickel Company, Inc., New York, New York, have been found suitable for this usage. Since the index of refraction of the thin deposit is nowhere near that of glass, its refractive interference pattern is considered minimal.

In the light exposure procedure, discrete areas of the coated panel are subjected to light radiated from the primary light source 51 which is attenuated by the coating 57, refracted by the lens 55, and directed through the mask aperture 27. The discrete areas of the photosensitive coating 43 which receive the exposure light radiation are light polymerized or hardened and adhere to the inner surface of the panel 31 forming a first pattern of the subsequent window area. With the shadow mask still in place, the above-described procedure is twice repeated to dispose each of the related two remaining window patterns making up the triadical groupings. For the separate exposure of'each of the respective window patterns, the optical system 49 is shifted substantially 120 degrees about thecentral axis 13.

After the three respective window patterns are thus exposed and polymerized, the shadow mask 25 is removed and the exposed coating 43 suitably developed to remove the web-like unpolymerized interstitial area. This development step provides a polymerized window pattern in the format of multitudinous polymerized areas surrounded by a connected web pattern of substantially bare glass. Following development, the patterned panel is overcoated with an opaque colloidal suspension of graphite, and then treated with an appropriate degrading agent and rinse to effect removal of the polymerized window pattern format. This degradation and removal of the polymerized window areas also loosens and removes the associated graphite which'is disposed thereon. Thus, there is produced an opaque interstitial web having multitudinous windows therein in the form of discretely defined bare glass areas. It is on these window areas that the respective coloremitting phosphor materials are subsequently conventionally disposed by techniques known to the art to complete the windowed screen structure.

In greater detail, the optical system 49 is designed to provide deposition of the window pattern in a manner that the respective electron beams in the operating tube will impinge thereinto. The system, having an axis 61, which is laterally offset from the central axis 13 by the distance k, incorporates therein a primary exposure light source 51 in the form of an elongated luminous arc 62 emanating between the electrodes 63 and 65 in a mercury vapor lamp 67. An example of a conventional lamp is type EH6 which emits a high value of UV'radiant energy in the 300-400 nanometer (nm) range. The primary light source 51 has a longitudinal axis 69 that is oriented substantially normal to the optical system axis fill. The light collector 53 is a conduit means such as a quartz rod which collects and trans fers, by internal reflections, a portion of the nonsymmetrical radiant energy produced by the source 51. Light emanating from the collector rod 53, as for example attenuated rays represented by lines 71 and 73, ultimately reach the photosensitized coating 81 to photoform like peripheral window areas 75 and 77, respectively; they being diagonally opposite areas of the screen. Even though a substantially concave-shaped reflector 79 is utilized, the exposure radiant energy emanating from the terminal end 81 of collector rod 53 is substantially of an elongated pattern. Since the intensity of the exposure illumination varies as the inverse square of the distance between the source and point of exposure, discrete compensation is required to attain annular uniformity of light intensity from the nonsymmetrical light source.

To compensate for the nonsymmetrical pattern of illumination, a discretely formed composite light attenuation coating 57 is disposed relative to a surface of the lens 55 in a manner to affect the exposure light transmitted therethrough. As illustrated in FIGS. 3 and 4, the composite light attenuation coating 57 is disposed in substantially the form of two superjacently related patterns directly on the surface of the lens 55, as, for example, by vapor deposition. Since the structure and detailed orientation of the lens 55 do not substantially influence the desired functioning of the discretely disposed coating 57, specific details of the lens or optical medium construction are eliminated from this specification and drawings relating thereto. The lens 55 has X and Y axes and a center plane therethrough substantially coincident with the Y axis and normal to the plane of the X and Y axes. The lens 55 is oriented in the optical system with its X axis substantially parallel with the longitudinal axis 69 of the elongated light source 511. The composite light attenuation coating 57 on the planar surface 83 of the lens 55, substantially covers the whole of the optical utilized surface in a differential density deposition of two related coating patterns. This discrete attenuation provides control of the exposure illumination in a manner to produce substantially constant window sizes for all three colors in annular orientation progressively about the central axis of the screen, and additionally effects a variable gradient of window sizes in a radial direction from the center to the periphery of the color screen structure. Considered as a whole, the composite attenuation pattern exhibiting differential translucency has been determined through extensive experimenation to achieve the desired compensation for the nonsymmetrical illumination emitted by the elongated source. Since the lens 55 is of high UV transmissive optical glass, the UV attenuation of the glass per se is of very low order, and is considered minimal in this instance.

With reference to FIG. 4, the first attenuation pattern of the composite coating 57 is comprised of substantially two parts 87 and 87', which affect primarily the Y axis region of the lens 55. The density of this coating pattern decreases in a gradual manner from the central region of the lens to the periphery thereof. The related second attenuating pattern of the composite coating 57 is generally of a gradual heavier density than that exhibited by the first pattern, and is in substantially the generic form of a modified lemniscate 89. The major dimension W of this lemniscate formation is oriented substantially in the lens transverse region related to the X axis thereof. The minor dimension 2 is oriented across the waist section 91 of the lemniscate substantially coincident with the Y axis of the lens 55. The heaviest or most opaque coating deposit of this second attenuation pattern 89 is substantially in the central area 93 of the lens 55 in the general region intersected by the axis of the optical system 61 with the density decreasing gradually outward therefrom to the periphery 95. This lemniscate coating formation 89 is formed on the lens 55 with substantially equi-sized lobe portions 97 and 99 disposed on either side of the center plane 101. The areas of heaviest coating density of the first attenuating pattern 87, 87' are adjacent the waist section 91 of the modified lemniscate formation 89.

With reference to FIG. 5, there is shown an exemplary profile 103 of the UV transmission of the composite attenuation coating 57 as evaluated relative to the center plane 101 along the Y axis of the lens 55 which, in this instance, has a inch diameter. As portrayed, disregarding the reflective factor of the glass, the differential ultraviolet transmission of the coating per se ranges from substantially 98 percent at the periphery 95 of the lens to substantially 16 percent in the center lemniscate area 93. The waist 91 of the lemniscate formation of coating 89 is evidenced as extending from substantially from -O.4 to +0.8 inches of the diametrical lens dimension. Similarly, the exemplary FIG. 6 illustrates a UV transmission profile 103 of the same composite attenuation coating 57 relative to the X axis of the same lens 55 as shown in FIG. 5. Across the lens on this axis, the differential UV transmission of the typical coating embodiment increases from substantially 98 percent at the periphery of the lens to substantially l6 percent in the central area 93. In this profile the expanse of greater attenuation in the lemniscate formation of coating 89 is evidenced with relationship to the major dimension W thereof as extending from substantially --l .0 to +1.0 inches of the diametrical lens dimension.

Deposition of the related discrete patterns comprising the composite light attenuation coating 57 is achieved by employing the vapor coating apparatus 107 illustrated in FIGS. 7 and 8. The apparatus, which has a vertical axis 108, includes an encompassing hermetic chamber 109 having a dome portion 111 and a matching base portion 113. Evacuation means (not shown) is connected therewith by conduit means 115 to achieve a predetermined degree of vacuum therein.

A metal vaporizing source or crucible 117 is oriented on the apparatus axis 108 within the chamber 109, by means not shown, relative to the chamber base portion 113. The vaporizing crucible 117, being of a ceramic material such as alumina, is formed to have a bottom portion 119 internally shaped substantially as a cone wherein tbe evaporable metal 120 is contained in substantially axial orientation to provide a uniform vapor stream froma quasi-point source. Upstanding from the peripheral circumference of the cone-shaped bottom 119 is a substantially cylindrical sidewall portion 121 that opens in an upward direction to form and direct a diverging vapor beam 123 thenceward. Contiguously associated with the crucible 117 is a controlled electrical heating means 125 in the form of a coiled conductor having connective leads 127, 127' extending without the chamber 109 to suitable control means, not shown.

Surrounding the crucible 117 is a vapor shield 129 having a top oriented opening or port 131 of a size to permit the vapor beam to project therefrom. Associated with the port of the shield is a movable shutter means 133 positioned relative to the port opening 131 to provide projection control of the vapor beam 123. The shutter is supported on a movable shaft 135 which permits external control of desired shutter positioning.

A rotatable first pattern mask 137 is spaced within the chamber above the vaporizing souce 117 in substantially the path of the vapor beam 123 to initially modify the beam passing therethrough. The first mask pattern 139 is a discretely shaped configurative opening formed in a thin rigid material, such as a metal plate 141. This plate, in turn, is suitably affixed to a rotatable supporting rim 143 having a circumferentially oriented groove 145 therein to accommodate the driving belt 147 of rotational linkage means 149. With particular reference to FIGS. 8 and 9, the first mask pattern is shown to be substantially formed as an altered cardioidal figure having a vertex 151 and a distal point 153 defining the maximum radius r" from the vertex which is oriented on the apparatus axis 108. The term altered cardioidal figure" is intended to include a hybridity of cardioidal and Archimidian spiral figures and modifications thereof. The significance of utilizing this type of figure will be described subsequently.

In the chamber 109, immediately above the first pattern mask 137 and related thereto is a movable second pattern mask 157 which has a second mask pattern 159 therein formed as a discretely shaped opening markedly differing from the first mask pattern 139. For example, this second mask pattern 159 is shown as a modified lemniscate configuration. This second pattern mask 157 is suitably supported in a movable shaft 161 which facilitates predeterminate insertion and removal of the second pattern mask into and out of the initially modified vapor beam 123'. Insertion of this pattern into the beam effects a secondary modification 123" of the beam 123'.

Oriented spacedly above the movable second pattern mask 157, within the chamber, are adjustable support means 165 fashioned to provide accurate positioning of an optical component or-medium 167, such as a lens or optical plate, to suitably receive the vapor deposition patterns on the under surface 169 thereof.

The distance between the evaporable metal 120 and the under surface 169 of the optical component 167 is shown in FIG. 7 as m n." The distance n" being that between the evaporable metal 120 and the movable second pattern mask 157, and the distance m being that between the second pattern mask 157 and the surface 169. It has been found advantageous to locate the second pattern mask at a position whereof n is substantially within the range of substantially 60-75 percent of the combined distance m n to provide desired feathering transition of the attenuating patterns comprising the composite attenuating coating 57.

Optical monitoring means 171 are oriented to direct a collimated beam of light into the chamber in a manner to substantially intersect the apparatus axis 108 at the plane of the positioned optical component 167. In greater detail, the optical monitoring means 171 comprises a source of radiant energy 173, such as a low voltge helium-neon laser generator capable of continuous operation. The collimated beam of predetermined radiant energy 175 projected therefrom is immediately directed into a time beam interruptor or chopper 177 which pulses the radiant energy to a modulated beam 175', as for example, 330 cycles/second. This pulsed beam is projected through an optical port 181 into the interior of the chamber 109. Within the chamber are cooperating beam reflective means, such as mirrors 183, 184, and 185, which are angularly and relatedly positioned by individual means, not shown, to direct the modulated beam 175' in a manner to impinge and traverse the positioned optical component 167 at substantially the axis of the apparatus 108. The modulated beam after traversing the optical component 167 impinges mirror means 185 and is directed through an exit optical port 187 in the chamber into beam receptor means 189 which is tuned to respond to the frequency of the modulated beam. Since the beam receptor is tuned to a particular frequency, ambient and other extraneous beams of light, such as light from the vaporizing source, are not accepted by the receptor unit. Associated with the receptor means 189 are beam interpretive means 191 for measuring the intensity of the emergent beam after passing through the attenuating coating 57 disposed on the under surface of the optical component 167.

In accomplishing the coating process, the optical medium 167 such as a lens 55 is positioned on the support means 165 in a manner that the axis of the lens substantially coincides with tbe axis of the coating apparatus 108. A portion of suitable evaporable metal 120, such as the aforementioned Inconel, is placed in the vaporizing crucible 117, and the shutter 133 closed to initially control the vapor stream and prevent the projection of possible vapor contaminants that may be expelled during the early stages of heating. The hermetic chamber 109 is closed and the evacuation means activated to achieve a vacuum of substantially 10 Torr, whereupon heating of the crucible 117 is initiated. Rotation of the first pattern mask 137 is started; the speed of rotation is not critical but should be constant. A low rpm. is preferred to reduce the possibility of initiating vibrations in the apparatus. The second pattern mask 157 is moved to an off-axis inactive position. When the temperature of the crucible 117 has reached the desired operating level, as for example l,800-2,000 degrees Centigrade, the shutter 133 is opened and the vapor beam permitted to project to the optical medium 167. Passage of the vapor beam 123 through the moving configurative opening 139 of the rotating first pattern mask 137 modifies the vapor stream and produces a symmetrical first deposition pattern 87, 87' on the optical medium 167 which is illustrated in FIG. 4 as lens 55.

In FIG. 9, two related shapings of the first mask pattern 139 and 139' are shown having breadths b and b respectively. As positioned in the apparatus 107, the vertex 151 is oriented on the axis 108. As the first pattern mask 137 rotates, the distal point 153 of the pattern influences the peripheral deposition on the lens. With reference to FIGS. 41, 5 and 9, use of the altered cardioidal mask FIG. 139 have a breadth b would substantially produce the first coating pattern 87, 87' on the lens 55, the transmission profile of which is shown in FIG. 5. In contrast therewith, use of a further altered mask FIG. 139 representing a smaller opening would result in a profile of decreased slope such as indicated by lines 88, 88' in FIG. 5. Thus, the slope of UV transmission of the first coating pattern is determined by the defined configuration of the pattern in the first rotatable first pattern mask 137.

Upon opening of the shutter 133, operation of the optical monitoring means 171 is initiated, and tbe intensity of the modulated light beam 175' passing through substantially the axis of the medium 157 (55), is received by beam receptor means 189 and interpreted by means 191. In referring to FIG. 10, there is shown a progressive light transmission profile 195 of the central portion of the coating disposed on the medium or lens 55. The monitoring means 171 is previously calibrated at percent transmission when the modulated beam 175 traverses the uncoated lens medium. Thus, as the coating 57 is disposed on the under surface 169 the light transmission decreases as the evaporation time increases. When the monitoring means 171 indicates the lens to have a central light area transmission within the range of substantially 16 to 20 percent, the second pattern mask 157 is inserted into the modified vapor beam. A preferable point of insertion 197 is shown at approximately 18 percent transmission. This stage of operation is illustrated in FIGS. 7 and 8. In the embodiment shown, the second pattern mask 157 represents a modified lemniscate configurative opening 159, but such is not to be considered limiting. In FIG. 5, the insertion of the second pattern mask is indicated on the transmission profile as indicated at substantially points 199, 199'. The evaporation of the metal is continued until the central area light transmission of the optical medium is within the range of substantially 10 to 15 percent. A preferable point of discontinuance 201 is shown at approximately 12 percent transmission, at which time the shutter 133 is closed and the apparatus properly deactivated.

Thus, there is described an improved process for achieving a controlled gradient density coating on a light attenuation medium advantageously employed in an optical system for photo-forming a color CRT composite screen structure.

The composite light attenuation coating thus disposed provides discrete control of the exposure illumination to effect substantially constant window sizes for all three colors in annular orientation progressively about the central axis of the CRT screen, and additionally provides a variable gradient of window sizes in a radial direction from center to periphery of the screen structure.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is: 1. A process for disposing a discretely patterned light attenuating coating on a substantially transparent optical medium having a central axis by utilizing a vacuum coating apparatus employing a hermetic chamber wherein a metal vaporizing source and open-patterned mask means are positioned along a substantially vertical axis, said process comprising the steps of:

positioning said optical medium in axial alignment in the hermetic chamber portion of said apparatus;

providing an evaporable metal therebeneath in said metal vaporizing source in axial orientation within said chamber;

orienting a rotatable open first pattern mask between said vaporizing source and said optical medium; providing a predetermined reduced pressure level within said chamber;

initiating rotation of said open first pattern mask;

evaporating said metal to form an axial related beam of metal vapor upwardly directed to be modified by said rotating first pattern mask;

permitting said modified beam to impinge said positioned optical medium, thereby forming a first coating pattern, the density of said first coating pattern decreasing in a gradual manner from the central region of the optical medium to the periphery thereof; and

inserting an open second pattern mask at a predetermined time into said modified beam of metal vapor intermediate said rotating first pattern mask and said optical medium to effect further modification of said beam before impingement upon said optical medium, thereby forming over said first coating pattern a second coating pattern being ofa generic shape differing from that of said first coating pattern to thereby form a composite metal coating of a controlled gradient density on said medium.

2. The process for disposing a patterned light attenuating coating on a substantially transparent optical medium according to claim 1 wherein the rotation of said open first pattern mask is continued during the coating process, and wherein said open second pattern mask is maintained in a non-rotatable manner after insertion into said modified vapor beam.

3. The process for disposing a patterned light attenuating coating on a substantially transparent optical medium according to claim 1 wherein said second pattern 7 percent. 

2. The process for disposing a patterned light attenuating coating on a substantially transparent optical medium according to claim 1 wherein the rotation of said open first pattern mask is continued during the coating process, and wherein said open second pattern mask is maintained in a non-rotatable manner after insertion into said modified vapor beam.
 3. The process for disposing a patterned light attenuating coating on a substantially transparent optical medium according to claim 1 wherein said second pattern mask is inserted into the vapor beam to further modify the same when a monitoring means in said apparatus indicates said optical medium to have a central area light transmission within the range of substantially 16 to 20 percent.
 4. The process for disposing a patterned light attenuating coating on an optical medium according to claim 3 wherein the evaporation of said metal is continued until the central area light transmission of said optical medium is within the range of substantially 10 to 15 percent. 